X-Ray Backscatter Mobile Inspection Van

ABSTRACT

Systems and methods for inspecting an object with a scanned beam of penetrating radiation. Scattered radiation from the beam is detected, in either a backward or forward direction, as is radiation transmitted through the inspected object. The source of penetrating radiation is concealed within an enclosure of a road-worthy vehicle, and detected with a large-area uncollimated detector similarly concealed within the enclosure.

The present application is a divisional application of copending U.S.Ser. No. 13/482,613, filed May 29, 2012, which is a divisional of U.S.Ser. No. 12/891,997, filed Sep. 28, 2010 and now issued as U.S. Pat. No.8,194,822. The latter application was a divisional application of U.S.Ser. No. 12/368,736, abandoned, which was a continuation-in-partapplication of U.S. Ser. No. 11/608,957, filed Dec. 11, 2006, now issuedas U.S. Pat. No. 7,505,556. The latter application was acontinuation-in-part application of U.S. Ser. No. 11/238,719, filed Sep.29, 2005, now issued as U.S. Pat. No. 7,218,704, itself a continuationapplication of U.S. Ser. No. 10/442,687, filed May 21, 2003, now issuedas U.S. Pat. No. 7,099,434, which was a continuation-in-part of U.S.Ser. No. 10/330,000, filed Dec. 26, 2002, and claimed priority from U.S.Provisional Application Ser. No. 60/424,357, filed Nov. 6, 2002, as doesthe present application. All of the foregoing applications areincorporated herein by reference.

U.S. Ser. No. 12/891,997, of which the present application is adivisional application, is, as recited above, a divisional of U.S. Ser.No. 12/368,736, abandoned, which was also a continuation-in-part of U.S.Ser. No. 11/551,991, filed Oct. 23, 2006, and issued as U.S. Pat. No.7,551,715, and claims priority, through that application, to U.S.Provisional Patent Applications Ser. No. 60/729,528, filed Oct. 24,2005, Ser. No. 60/729,548, filed Oct. 24, 2005, and Ser. No. 60/748,909,filed Dec. 9, 2005. All of the foregoing applications are incorporatedherein by reference.

TECHNICAL FIELD

The invention generally relates to inspection systems based upondetection of penetrating radiation from within an enclosed conveyance.X-Ray Backscatter Mobile Inspection Van

BACKGROUND OF THE INVENTION

X-rays are currently employed for the inspection of cargo containers,including motor vehicles, freight pallets, etc. Current technology,however, typically requires that some structure associated with theinspection system be disposed on either side of the inspected object.Thus, for example, a source of x-rays may be disposed distally withrespect to the inspected object while a detection system disposedproximally to the inspected object characterizes the x-rays which havetraversed the inspected object. In other modes of x-ray inspection,described in U.S. Pat. No. 6,292,533, issued Sep. 18, 2001 andincorporated herein by reference, a source of penetrating radiation ismounted on a moveable bed which is driven by a stationary cargocontainer, while a boom extends either a detector or a beam stop to thedistal side of the cargo container. Current technology, in summary,requires that the inspected objects or persons either be moved throughan inspection system or interposed between a proximal examiningcomponent and a distal examining component, one including a source andthe other including a detector.

An effective means, however, is desirable for non-intrusively examiningpersonnel as well as the interior of vehicles, cargo containers, orother objects. In particular, with respect to cargo enclosures, it isdesirable to detect the presence of people, potential contraband,threats, or other items of interest, without imposing the requirementsand constraints of current systems. Combining such an examination withpassive sensing of radioactive or fissile material would also beadvantageous.

The resolution of information obtained about the interrogated object orperson is dependent upon a variety of factors including the distancebetween the inspection system and the object, and the magnitude andenergy spectrum of the x-ray flux. In current systems, as the distancebetween the X-ray system and the object increases or as the fluxdecreases, the image resolution and quality (as manifest in thesignal-to-noise, for example) decreases. The decrease in quality issubstantially caused by the reduction of backscattered flux captured bythe detectors. Current backscatter x-ray imaging systems locatedetectors adjacent to the x-ray source, allowing the combined system ofsource and detectors to be as close as possible to the object beinginspected. The proximity of the system to the object creates a highquality image without the need for a high x-ray flux.

However, there are many applications, especially security andsurveillance applications, where a larger distance between the imagingsystem and the object to be inspected would be desirable. One suchapplication is where personnel to be inspected might be carryingexplosive devices carried under clothing or concealed in backpacks orbags and the risk of suicide detonation is present. Suicide bombingshave often entailed large quantities of metal shrapnel packed around theexplosive to maximize the lethality of the device, typically nuts,nails, or ball-bearings.

Current x-ray inspection systems are often inadequate in suchapplications and are rarely used in applications requiring distancesgreater than five feet. Current systems can counteract the decrease inimage quality by increasing the size of the detectors or using higherflux x-ray sources. However, if the distances are too great, thedetectors required will be impractically large. Additionally, as theflux increases, so will the objects exposure, which poses a problem whenthe object is, or may contain, a person.

One scenario for backscatter inspection from a mobile inspection vehicleis described in U.S. Pat. No. 7,099,434, to Adams et al., issued Aug.29, 2006 and incorporated herein by reference. Embodiments of thatinvention can be highly effective at detecting large quantities ofexplosives or other organic materials in vehicles or other containers.One consideration, however, is that metal objects (such as artilleryshells) within a metallic container (such as a vehicle) may not bewell-detected unless favorably silhouetted against a brightly scatteringbackground of organic material.

Another issue for backscatter technology is that it can sometimes bedifficult to image organic materials when they are placed within orbehind significant amounts of high-Z material, such as steel. An exampleof this might be a small quantity of explosive concealed in the trunk ofa vehicle. Because the backscattered x-rays are typically detected inthe backward direction (scatter angles typically in the range)140°<

<180°, the average energy of the scattered x-rays is quite low (about 68keV for a primary x-ray beam from a 225 kV x-ray source). Theselow-energy x-rays are then greatly attenuated by the steel body of thevehicle, resulting in a greatly reduced number of scattered x-rays beingdetected in the backscatter detectors. This problem is often exacerbatedbecause the scattered x-rays reach backscatter detectors having passedthrough an intervening steel surface at an oblique angle, resulting inan effective thickness of steel that is greater than the actual gauge ofthe steel.

SUMMARY OF CERTAIN EMBODIMENTS OF THE INVENTION

Representative embodiments of the present invention include a system anda method for inspecting an object.

In accordance with one aspect of the invention, in one of itsembodiments, there is provided an inspection system for inspecting anobject. The object of inspection may be a person, for example, but mayalso be cargo or a vehicle of any sort. The inspection system has anenclosed conveyance, such as a van or other vehicle, characterized by anenclosing body. Additionally, the system has a source of penetratingradiation contained entirely within the body of the conveyance forgenerating penetrating radiation for forming the penetrating radiationinto a beam for irradiating the object. A detector, also containedentirely within the body of the conveyance, is provided for generating ascatter signal based on penetrating radiation scattered by contents ofthe object. Finally, the system has a controller for ascertaining aspecified characteristic of the scattered radiation. Additionally, animage generator may be provided for forming the signal into an image ofthe contents of the object based in part on the scatter signal and therelative motion signal.

In accordance with further embodiments of the invention, the conveyancemay include a vehicle capable of road-travel. The source of penetratingradiation may include an x-ray tube, more particularly, an x-ray tubeemitting radiation at energies below approximately 250 keV. The sourceof penetrating radiation may include a rotating chopper wheel emittingradiation to one or both sides of the enclosed conveyance.

In accordance with yet further embodiments of the invention, theproximity sensor may be chosen from the group of sensors includingradar, ultrasound, optical, laser, and LIDAR sensors. A detector, whichmay be separate or the same as one of the scatter detectors, may alsoexhibit sensitivity to decay products of radioactive or fissilematerial, and may be sensitive, particularly, to neutrons or gamma rays.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will be more readily understoodby reference to the following detailed description taken with theaccompanying drawings:

FIG. 1 is a perspective view, cutaway in part, of a mobile cargoinspection system deployed on a truck capable of on-road travel andscanning of an enclosure such as a vehicle or cargo container while oneor both of the inspection system and enclosure are in motion, inaccordance with preferred embodiments of the present invention;

FIG. 2 is an image of various vehicles as imaged in backscatterradiation by the system of FIG. 1 in accordance with an embodiment ofthe invention;

FIG. 3 is a schematic representation of an inspection vehicle, inaccordance with embodiments of the present invention, providinginspection capability to either side of the vehicle;

FIG. 4 is schematic representation of an embodiment of the invention inwhich a source of penetrating radiation and detection modules areconcealed within a container;

FIG. 5 shows a modular configuration of an inspection system in whichdistinct functional components of the inspection system are disposedwithin coupled modules;

FIG. 6 is a side view of an inspection system deployed from within aself-contained trailer;

FIG. 7 is a rear view of the trailer-borne inspection system of FIG. 6;and

FIG. 8 shows a transmission detector placed at the far side of a vehiclebeing imaged according to one embodiment of the present invention.

FIG. 9 shows a forward scatter detector placed underneath a vehicle forimaging according to one embodiment of the present invention.

FIG. 10 shows incorporation of a horizontal section of a transmissiondetector and forward scatter detectors into a rapidly deployable“speed-bump” according to one embodiment of the present invention.

FIG. 11 shows various functional components according to a “Z-Radar”™embodiment of the present invention.

FIGS. 12A and 12B show aspects of various signal calibration schemes asused in specific embodiments.

FIG. 13 shows details of an embodiment in which several interrogationpoints are rapidly established.

FIG. 14 shows an inspection system designed to inspect personnel.

FIG. 15 shows an inspection system designed to inspect walls of abuilding for foreign objects.

FIG. 16 shows an inspection system designed to located people in anadjacent room with detectors built into the walls of the room.

FIG. 17 shows an inspection system designed to locate people in anadjacent room with detectors located in rooms adjacent to the room ofinterest.

FIG. 18 shows an inspection system designed to extend the range ofexisting inspection systems by relocating detectors closer to the objectbeing inspection.

FIG. 19 shows an inspection system with the source of penetratingradiation and detectors located on vehicles capable of road travel.

FIG. 20 shows an inspection system designed to inspect possible IEDswith the detector located on a forward deployed robot.

FIG. 21 shows a top view of an inspection system with the source ofpenetrating radiation mounted to a swivel mount on a vehicle capable ofroad travel and the detector mounted on a drone vehicle.

FIG. 22 shows a side view of an inspection system with the source ofpenetrating radiation mounted to a swivel mount on a vehicle capable ofroad travel and the detector mounted on a drone vehicle.

FIG. 23 shows an inspection system for inspecting suspect travelers withthe x-ray source mounted in the ceiling.

FIG. 24 shows an inspection system for inspecting passing cars with thedetectors located along the roadway and the x-ray source mounted abovethe roadway.

FIG. 25 shows a top view of the detector located in the ground withstructural support.

FIG. 26 shows a side view of the detector located in the ground withstructural supports and camouflage layer.

FIG. 27 shows a side view of an inspection system with an array ofdetectors, located in the ground, surrounding the x-ray source.

FIG. 28 shows a top view of an inspection system with an array ofdetectors, located in the ground, surrounding the x-ray source.

FIG. 29 shows a top view of an inspection system where the detectors arefree standing monoliths.

FIG. 30 shows an inspection system in which the signals from detectorsat different distances are separated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

X-ray scattering may be employed for inspection of personnel, vehicles,cargo, or other objects of interest. The term “object” is usedinclusively herein to encompass any of the above. In systems employingx-ray scattering, x-rays are formed into a beam that is directed towardsthe object of interest. When the beam hits the object, scattered X-raysare captured by x-ray detectors and various characteristics of thescattering object may be ascertained, either globally, or with respectto a pixelated image of the object.

As used in this description and in the appended claims, a “cargocontainer” is a receptacle for the storage or transportation of goods,and includes freight pallets as well as vehicles, whether motorized ordrawn, such as automobiles, the cab and trailer of a truck, railroadcars or ship-borne containers. The term “cargo container,” as usedherein, further includes the structures and components of thereceptacle.

The invention described herein serves to characterize materials whichmay be contained within a cargo container and thus not readilysusceptible to visual scrutiny, or, alternatively, may be carried on theperson of a human or on another animate subject. The characteristics ofa material which might be the object of non-invasive inspection andwhich lend themselves to detection using the device and method taught bythe invention include, but are not limited to, electron density, atomicnumber, mass density, linear dimensions and shape. These characteristicsare unveiled by taking advantage of the various physical processes bywhich penetrating radiation interacts with matter. Penetrating radiationrefers to electromagnetic radiation of sufficient energy per photon topenetrate materials of interest to a substantial and useful degree andinclude x-rays and more energetic forms of radiation. The interaction ofsuch radiation with matter can generally be categorized as eitherscattering or absorption processes. Both types of process remove x-rayphotons from a collimated (i.e., directional) beam; scattering processesdo so by deflecting photons into new directions (usually with loss ofenergy), while absorption processes simply remove photons from the beam.

Description of the rudiments of a mobile inspection system is to befound in U.S. Pat. No. 5,764,683, issued Jun. 9, 1998, and incorporatedherein by reference. As used in this description and in any appendedclaims, the term “source” is used in a broad sense to encompass theentirety of the apparatus used to generate a beam of penetratingradiation that is used to irradiate the object under inspection. Thesource is taken to include the generator of penetrating radiation (the“source”, in the narrow sense) which may include an x-ray tube or aradio-isotope. It is, furthermore, to be understood that the term“source” as used herein and in any appended claims, and as designatedgenerally by numeral 30 in the drawings, refers to the entirety of theapparatus used to generate beam 24, and may have internal componentsthat include, without limitation, apertures, choppers, collimators, etc.

Scatter imaging in which the x-rays scattered by a material (typicallyin a generally backward direction) are employed offers several uniqueinspection capabilities and operational features. Scatter imaging allowsimages to be obtained even when the imaged object is accessible fromonly one side. Moreover, since the scatter signal falls off quiterapidly with increasing depth into the object, backscatter imageseffectively represent a “slice” of the object characteristic of the sidenearest to the x-ray source, thereby reducing problems of image clutterthat may confound transmission images. The Compton effect, whichdominates x-ray scatter in the energy range typically employed inaccordance with the present invention, dominates the interaction ofx-rays with dense low-atomic-number (low-Z) materials. Narcotic drugstend to produce the bright signatures in a backscatter image, as doorganic explosives, making backscatter imaging a useful imaging modalityfor bomb or drug detection. Finally, alignment requirements of the x-raybeam with detectors or collimation devices are less exacting than fortransmission imaging thereby enabling rapid deployment in a wide rangeof inspection scenarios.

Flying-spot technology makes possible the acquisition of images usingdetectors specifically positioned to collect the scattered x-rays. In atypical flying-spot system, a thin “pencil beam” of x-rays is rapidlyand repetitively swept through a source-centered, vertically-oriented“fan” of beam paths that are arranged to intercept the object underinspection. At the same time, the object is moved at a constant, slowerspeed along a path perpendicular to the fan, on a horizontally movingconveyor belt for example. In this way, the pencil beam is made totraverse the object in point-by-point raster fashion, and the entireobject is scanned as it passes through the fan plane over a periodranging from a few seconds to a few minutes depending upon the length ofthe object.

Although the total scan time may be seconds to minutes in duration, theactual exposure time of any part of the scanned object is only the brieftime it takes for the pencil beam to sweep across a given pixel. Thatexposure time is typically in the range of microseconds, depending onthe design and the application, and yields an entrance exposure to thescanned object that constitutes a low dose to the object also means thatthere is little radiation available to scatter into the environment, sothe doses to operators and other bystanders is correspondingly low.

Referring now to FIG. 1, various embodiments of this invention make useof systems in which detectors are mounted on a mobile platform 710, orconveyance, typically capable of road travel, that traverses a largeobject to be inspected such as a vehicle or a cargo container 712.Conveyance 710 is characterized by an enclosure 714, here, the skin of avan, shown, in cutaway view, to enable depiction of other components ofan inspection system. The conveyance can have many alternateembodiments, including but not limited to gasoline, diesel, electric,propane, battery, fuel-cell, or hydrogen-powered motor vehicles(including vans, trucks, or similar), tracked vehicles, sleds, trailers,cranes, or other equipment that can be put into motion, preferablyself-propelled, but also including vehicles tethered and pulled such asunder electric power.

Contained within enclosure 714 of conveyance 710 is a source 730including x-ray tube 732 (shown in FIG. 3) and chopper 734. Inaccordance with preferred embodiments of the invention, source energiesare typically below 250 keV, thus the chopper 734 may be smaller thanemployed in current systems in which higher-energy x-rays are employed.Chopper 734 may be a rotating perforated hub, or a wheel withtransmitting spokes, or any number of means, known in the art, forgeneration of flying spot beams that lie, typically, in a planeapproximately orthogonal to the direction of motion 720. The x-ray tube732 depicted in FIG. 3, by way of example, is a panoramic-style x-raytube that is capable of wide-angle beam generation and additionally maybe rotatable to allow scanning on either side of conveyance 710.Rotating hoop 734, with apertures 736 and 738, emits a pencil beam 724,thereby enabling inspection of objects, possibly on either side of theconveyance, herein referred to as “bilateral” inspection. However, allsources are encompassed within the scope of the present invention whenemployed in the manner described in the present description. The x-raysource and detectors may be oriented to permit scanning from theconveyance's “driver's side”, “passenger's side”, or both sidessimultaneously.

Various means are known in the art for mechanically or electronicallysweeping a beam of penetrating radiation, including, for example, therotating chopper wheel 734 depicted in FIG. 3 or electronic scanning isdescribed in detail, for example, in U.S. Pat. No. 6,421,420, issuedJul. 16, 2002, which is incorporated herein by reference. In embodimentsemploying a mechanical rotating chopper wheel 734, as the chopper wheelrotates in the direction of arrow 722, penetrating radiation 724 emittedfrom the target of x-ray tube 732 passes successively through aplurality (typically, three or four) of channels. Wheel 734 isfabricated from a material, typically lead, that blocks transmission ofx-rays except through apertures 736, 738. X-rays 724 emerge from thecurrently illuminated channel as a pencil beam that is swept acrossobject 712 undergoing inspection as wheel 734 rotates. The dimensions ofthe beam 724 typically govern the resolution of a system such as the onedepicted. Aperture 736 may have various shapes, and may be circular orrectangular, and may be more specifically tailored. Other x-raygeneration approaches may be used to produce a similar sweeping pencilbeam, such as spinning discs with elongated slits, wheels with hollowspokes, are alternate embodiments.

Detector modules 100 are carried by conveyance 710 and typicallyenclosed within enclosing body 714 and concealed from view from outsidethe conveyance. They may also be carried outside the conveyance forparticular applications within the scope of the present invention.Detector modules contain detectors for detecting penetrating radiationfrom source 730 that has interacted with, and scattered from, contentsof the inspected object 712.

The source of scattering may be characterized as anomalous for thenature of the person or item being scanned. Thus, a person 50 (shown inFIG. 2) carrying explosives may be detected on the basis of locallyenhanced x-ray scatter. A specified characteristic of the scatter, suchas a localization or particular disposition with respect to theinspected object, may be ascertained in order to determine threat levelsof the object.

Detector modules 100 may also be sensitive both to emission naturallyemitted by threat materials, as further described, for example, incopending U.S. patent application Ser. No. 10/156,989, filed May 29,2002, entitled “Detectors for X-Rays and Neutrons,” which isincorporated herein by reference. In accordance with various embodimentsof the present invention, a detector is employed of the type having highefficiency for detecting thermal and epi-thermal (intermediate energy,typically 1-10⁴ eV) neutrons. The detector uses the scintillator Gd₂O₂S,commonly known, and referred to herein, as “gadox,” to stop bothneutrons and the photons. X-ray-induced scintillations from the gadox inthe visible portion of the spectrum are then detected, typically byphotomultipliers or photodiodes. Alternative scintillators, such as LiF,for example, with high cross sections for detecting thermal andepithermal neutrons are also within the scope of the present invention.

Separate, large-area detectors are deployed adjacent to the beam planeon the x-ray source side of the scanned object, and with their activesurfaces oriented toward the scanned object. These detectors need onlyprovide a large solid angle for collection of scattered radiation; nocritical alignments are required. In this location these detectorsrespond to x-rays which are scattered generally back toward the sourcefrom the object.

FIG. 3 shows a schematic top view of another embodiment of the inventionthat may advantageously be employed for the inspection of objectsdisposed to either side of the inspecting conveyance.

In accordance with the present invention, various inspection modalitiescurrently in use for detection of contraband materials may additionallybe used for finding fissionable material in the containers they examine.Some methods are passive; i.e., the emission of neutrons or gamma raysfrom radioactive materials may be signatures for an alert. Severalmethods for carrying out such passive measurements are described incopending U.S. Provisional Application Ser. No. 60/396,034, filed Jul.15, 2002, and incorporated herein by reference. Other methods areactive; i.e., penetrating radiation irradiates a container therebyexciting fluorescence of the fissile material and the characteristicx-rays of uranium or plutonium produce an alert signal.

Inspection of object 712 may be conducted by an operator disposed withinconveyance 710, or, alternatively, by a remotely disposed operator. Forinspection, object 712 may be maintained in a stationary condition, withconveyance 710 traversing the object along direction 720 (forwards orbackwards), alternatively, inspection may be conducted while bothconveyance 710 and inspected object 712 are in motion. In yet anothermode, referred to as a “portal mode,” the system is stationary and theobject of inspection is conveyed past the system. Where the object ofinspection is a person, the person may be required to walk past theconveyance slowly, preferably in both directions, so that both sides ofthe person can be subjected to search.

Referring further to FIG. 3, the x-ray beams in x-ray inspection systemstypically sweep, as by rotation of chopper wheel 734, through theinspection volume during a large fraction of the operating time. Duringthe remaining fraction of each sweep cycle there are essentially nosource x-rays striking the target container. Thus, during the time ofsource quiescence, the detectors are only counting background.

In a preferred embodiment, particularly useful for lower energy (140keV-160 keV) x-ray systems, the output from backscatter detectors 100are switched to a pulse counting circuit during the fraction of theoperating cycle during which the source of x-ray irradiation is off.During this period, individual neutrons or gamma rays can be detectedand analyzed. The efficiency of the backscatter detectors of an x-rayinspection system for detecting neutrons or gamma ray has been discussedabove.

Referring only to gamma ray detection for purposes of illustration, the186 keV gamma rays are emitted in 53% of the decays of ²³⁵U but only athin layer of the bulk uranium is accessible since the mean free path of186 keV gammas in uranium is only 0.36 mm. Still, every squarecentimeter of 10% enriched uranium will emit ˜two thousand 186 keV gammaphotons per second, giving rise to a count of 2,000×0.004=8 counts forevery square centimeter of surface area of uranium that faces thedetectors. A 1″ cube of uranium (weighing ˜¾ pounds) would signal itspresence with ˜50 counts in the 0.2 second off-period of the inspection.A signal of this magnitude is easily discriminated. The signal strengthis further increased by increasing detection efficiency, enlarging thedetectors, and increasing the off-time of the sweeping x-ray beam.

In a “stationary mode,” both the system and the object being scanned arestationary, and a vehicle-mounted x-ray scanning method, configured as apart of the system itself, is employed to create in effect bothhorizontal and vertical scanning to generate a backscatter x-ray image.Such methods may include the use of an x-y translation stage,electronically-steered x-ray sources (as described, for example, in U.S.Pat. No. 6,421,420, or other means.

In other embodiments of the invention, now described with reference toFIG. 4, a source of penetrating radiation, including x-ray tube 732 andchopper 734, as well as scatter detector modules 100 are included withina static imaging module 800, shown with its top panel removed forconvenience of depiction. In practice, it is advantageous that allcomponents of the x-ray inspection system be concealed within imagingmodule 800, so as not to be discernable from outside the module. Imagingmodule 800 is advantageously a standard shipping container (such as aTRICON triple container, standardized for ground and air transport), andmay contain attachment points for helicopter deployment to a locationwhere it remains static for some duration.

The x-ray beam is swept in a vertical swath, depicted schematically bythe partial plane designated by numeral 802. An inspected object 804,exemplified here by a vehicle, is scanned by x-rays as it traversesplane 802. X-rays scattered by object 804 are detected by detectormodules 100, which x-rays transmitted, or forward-scattered, throughobject 804 and detected by transmission or forward-scatter detectors(not shown) disposed within a forward-detection housing 806.

In accordance with preferred embodiments, imaging module 800 is deployedoperationally in conjunction with one or more other containers, as shownin FIG. 5, such as power module 500 and operator module 502, containingan operator console 504, all intercoupled by power and telemetryconnections for coupled operation.

FIG. 6 shows a side view of an embodiment of the invention, in whichdetector modules are operationally deployed outside, rather than within,an enclosure 600, where, in this embodiment, the enclosure is a trailerthat may be drawn to the site of operation behind a vehicle. FIG. 7shows a rear view of the embodiment of FIG. 6.

Forward Scatter Detection in Backscatter Inspection Scenarios

Detection, using illumination by penetrating radiation, either from amobile platform such as the Mobile Inspection Van described in U.S. Pat.No. 7,099,434, or from a fixed platform such as the Ruggedized DetectionImaging Module™ (RDIM), may be enhanced with respect to the detection ofmetal objects, such as might be concealed, for example, within a metalcontainer. Embodiments of the present invention offer improved detectionof a metal object within a metal container by adding a stationarytransmission detector on the other side of the object being scanned witha pencil beam, where the source of the pencil beam, and eitherbackscatter, forward scatter, or transmission detectors are concealedfrom view from the vantage of the inspected object.

Thick metallic materials disposed can be clearly seen in thetransmission image, derived as shown in FIG. 8, where attenuated, orblocked, transmission is due to the high attenuation of x-rays in thesematerials. As used herein, the term “metallic” is a proxy for materialsof high “Z”, where Z represents the atomic number characteristic of thematerial. For example, artillery shells will appear as very dark objectsin the transmission image, with little or no x-rays penetrating throughthem. Note that this can be done when the Mobile Inspection Van 400 isoperated either in motion or in the stationary portal mode. FIG. 8depicts source 402 and backscatter detector module 404 disposed withinMobile Inspection Van 400, and x-ray beam 406 scanning object 408.Transmission detection module 410 is here comprised of an uprightvertical segment 412 and a horizontal segment 414.

One way to help mitigate the problem of imaging organic materials withinor behind significant amounts of high-Z material (such as metal) is toadd some forward-scatter detectors 500 as shown in FIG. 9. Because theforward-scattered x-rays 510 detected in these detectors have only beenscattered through small angles (typically in the range of scatteringangles, (5°<

<30°), the average energy of the forward-scattered x-rays issignificantly higher than the energies of backscattered x-rays (whichare typically no greater than about 90 keV for a primary x-ray beam froma 225 kV x-ray source). This is due to conservation of momentum in theCompton scattering process. The higher energy of forward-scatteredx-rays allows them to more easily penetrate the steel in the vehiclebody and be detected. The signal from the forward-scatter detectors caneither be combined with the backscatter signal, or it can be displayedseparately to the operator.

A method for integrating the horizontal section of the transmissiondetector 414 and the forward scatter detectors 500 into a rapidlydeployable module is shown in FIG. 10. The detectors have beenintegrated into a re-locatable “speed bump” 600 which can beconveniently stored inside the back of the Mobile Inspection Van andwhich is placed on the roadway prior to commencing scanning vehicles. Ifnecessary, the speed bump can be conveniently broken down into threesmaller modules for storage and ease of handling. The vertical leg ofthe transmission detector would be a separate unit set up on the farside of the vehicle being scanned. X-ray beam axis 602 is shown.

It should be noted that all the claims made in this disclosure areapplicable not only to the Mobile Inspection Van as in the earlierreferenced patent application, but also to any application of radiationbackscatter technology, such as in a ruggedized shipping container thatcontains similar subsystems as a Mobile Inspection Van.

Returning now to embodiments of the invention in which the relativemotion of conveyance 710 and object 712 (shown in FIG. 1) may becarefully controlled or may be monitored by sensor 718 which employs anyof a variety of sensing methods, such as radar, ultrasound, or optical,including laser or LIDAR sensing, all provided as examples only, inorder to sense the relative speed of conveyance 710 with respect toobject 712. A signal provided by sensor 718 is employed by controller740 in one or more of the following modalities:

The vehicle speed may be regulated, or, alternatively, the pixelregistration may be corrected to compensate for vehicle speed anomaliesso as to produce aspect-ratio-correct, distortion-free, backscatterx-ray images. Relevant techniques include but are not limited to:

-   -   Use of high precision speed-sensing devices to accurately        measure vehicle speed at low (0.5 to 10 mile-per-hour) ranges;    -   low-speed (0.5 to 10 mile-per-hour) electronic and/or        software-based engine and/or transmission controls;    -   custom vehicle drive-train gear design, which simultaneously        produces low vehicle scan speed while maintaining the capability        of offering roadworthy speed ranges, up to at least 55 miles per        hour. In this context, the cruise-control system of a vehicle        may be ‘co-opted’ to govern motion at low scanning speeds.    -   over/under-speed indications to the driver, using high-precision        sensing devices coupled to a dashboard indicator, which the        driver uses to manually adjust throttle and braking to maintain        the desired vehicle speed within the range necessary to maintain        distortion-free images;    -   friction drive for driving the wheels of the inspecting vehicle        during inspection operations;    -   dynamic on-the-fly software correction. This method does not        attempt to regulate vehicle speed but rather uses real-time        high-precision vehicle speed and speed variation data from        on-vehicle sensor(s), of which a tire-driven embodiment is        designated by numeral 26, together with software algorithms        which interpolate, average or in other ways correct for the        aspect ratio distortion in the x-ray image data produced by        off-speed or varying speed.    -   Remote sensing of the object's speed using one or more of a        variety of sensors 718 and using signals generated by sensor 718        in software algorithms together with the vehicle speed data to        effect dynamic aspect ratio correction of the backscatter x-ray        image.

The foregoing methods for control and correction of relative motionvariations may be used either singly or in combination, within the scopeof the present invention. Sensors 718 may additionally provide forcontrol of x-ray beam direction such that the relative speed and trackangle of the source with respect to the scanned object may be activelytracked. This capability may advantageously allow improved images to beformed at faster speeds and, additionally, allow for relative motionthat is not purely unidirectional. It should be noted, additionally,that in circumstances where no horizontal spatial resolution isrequired, detection of relative motion is obviated.

FIG. 2 depicts a row of five vehicles scanned by a system as describedin the present application, showing concealed contents of the vehiclesin the various cases.

In the drive-by case, dosage to stationary people is readily reducedbelow regulatory thresholds provided vehicle speed is maintained above aspecified minimum while x-rays are on. An interlock is provided to cutoff x-ray generation when vehicle motion ceases or falls below aspecified minimum speed. Otherwise, x-rays may be enabled regardless ofproximity to objects.

For the stationary case, or for drive-by cases where additional safetymeasures are required or desired, proximity sensors, such as laser,microwave, ultrasound, or thermal sensors, for example, may be employedto determine the presence of objects to be scanned, enabling x-rays onlywhen necessary, and/or to discern if humans are in the beam path. Thesesensors typically operate all the time, with their signals processed viasoftware and/or hardware to intelligently control x-ray generation. Theoperator may also be provided with a manual “x-ray enable/deadman”control, in addition to any other safety devices and controls.

Features of the present invention may advantageously be employed inapplications including, but not limited to, the following:

-   -   Inspection/manifest verification of containerized, palletized,        or other packaged cargo, trucks or trailers being transported        across or staged at ports, borders, air terminals, or similar        transportation sites.    -   Verification that containers, objects, or vehicles are empty as        claimed.    -   Inspection of vehicles attempting to enter controlled or        high-value areas such as military bases, power plants, tunnels,        air terminals, public or government buildings, parking garages,        lobbies, service or delivery areas, tollbooths, or other        important installations, for contraband or threats such as        explosives, weapons, or smuggled personnel.    -   Inspection of vehicles or containers parked in garages, lots, or        on public or private thoroughfares for explosives, weapons,        contraband, or other threats.    -   Inspection of vehicles in motion for threats, contraband, or to        verify contents.    -   Inspection of objects potentially containing radioactive        materials that produce neutrons and or gamma rays.    -   Searching surrendering soldiers/civilians to ensure they are not        wired.    -   Searching personnel at border crossings/checkpoints to screen        out suicide bombers.    -   Scrutinizing persons in large groups.

Distant Detection of Backscatter

Embodiments of the present invention (which may be referred to as“Z-Radar”™) are now described with reference to FIG. 11. A backscatterinspection system, designated generally by numeral 900, use a collimatedbeam 102 of penetrating radiation, such as x-rays, to illuminate anobject 104 (which, as indicated above, may include a person) atrelatively large distances, to determine, for example, the metalliccontent on or within the object. An object will be said to be disposedat a “large distance” if the object of inspection, or a relevant portionthereof, subtends an angle of less than 5° in any direction as viewedfrom the source of illumination. Penetrating radiation may also include,for example, waves in other portions of the electromagnetic spectrum,such as gamma rays, but will be referred to, herein, as x-rays, withoutintended loss of generality. When the penetrating radiation is comprisedof x-rays, the x-rays may be generated by an x-ray source such as x-raytube 110.

Penetrating radiation 106 scattered by the inspected object is detectedin large-area x-ray detectors 108, and the signal generated by detectors108 is compared, by controller 112, with the expected signal fromorganic objects illuminated with x-rays at that distance. Objectscontaining metals absorb the x-rays, resulting in a backscatter signalwhich is lower than the signal expected from a purely organic object.

Inspected objects can include without limitation people or any objectwhich consists mostly of organic material, on or within which adetermination of the metallic content is desired. For example, themetallic shrapnel used by a suicide bomber to maximize the lethality ofthe explosive being carried may be detected, or the presence of metallicweapons, such as guns and knives may be detected.

In some embodiments, the object to be examined is initially located andtracked with a system utilizing one or more video cameras 114, althoughany other optical or non-optical means may also be employed, within thescope of the invention. FIG. 11 shows various functional componentsaccording to one specific embodiment of the present invention. Videocameras 114 of an optical surveillance system monitor an area ofinterest. A steerable x-ray source 110 is mounted on a base 116 whichcan rotate and translate the position of a penetrating x-ray beamgenerated by x-ray tube 110. Backscatter detectors 108 detect thebackscattered x-rays 106 from the target object 104 being illuminated.The video tracking system may be used to point the x-ray beam onto theobject of interest. A shutter (not shown) can then be opened to allowthe x-rays to briefly illuminate the target object for a pre-determinedtime period (known as the interrogation time). A data acquisition systemrecords the intensity of a signal received from the backscatterdetectors.

Referring now to FIGS. 12A and 12B, in order to accurately calibrate thebackscatter signal intensity, several illumination points (or“interrogation” points) 202, 204 can be chosen on the target 200, or onsimilar targets at the same distance. If the signal from one or moreinterrogation points appears significantly lower than that from theother interrogation points, it can be used to indicate the presence ofmetallic materials. On that basis, in accordance with embodiments of theinvention, a descriptive category is determined, such as that of aheightened security threat according to pre-established security threatcriteria, and appropriate action can then be taken accordingly.

Embodiments may also be suitable for determining the presence of organicmaterials on or within objects which largely consist of metallicmaterials. An example of this could be looking for explosives concealedin the door of a vehicle. For this application, interrogation pointswith a higher than expected signal are indicative of the presence ofconcealed organic material.

For objects which are relatively close to the x-ray source, thebackscatter signal can also be used to detect the presence of denseorganic material (such as explosives) concealed on an organic targetobject with a lower density. These materials tend to backscatter x-rayssomewhat more strongly than less dense organic materials, such as thehuman body.

In Table 1, the results of a computer simulation are shown for an x-raybackscatter interrogation system operating at three source voltages of160 kV, 450 kV, and 1.2 MeV. The simulations involved looking at thebackscatter signal from a person at various distances, and comparing thesignal with the signal from a person carrying a steel sheet or a personcarrying PETN explosive containing ball-bearings as shrapnel. The signalto noise ratio (SNR) is defined by:

${SNR} = \frac{N_{Person} - N_{{Person} + {Steel}}}{\sqrt{N_{Person}}}$

where N_(Person) is the number of detected backscattered x-rays from aperson carrying no steel and N_(Person+Steel) is the number of detectedbackscattered x-rays from a person carrying steel. It can be seen thatthe performance of the 225 kV and 450 kV systems is essentially thesame, but considerably better than the performance of the 1.2 MV system.Since a 160 kV system would be much cheaper and more compact than a 450kV system, a preferred source voltage is about 160 kV. The followingTable indicates the results of a computer simulation showing thesignal-to-noise ratio for detecting metal on a person (in the form of asteel sheet or a matrix of 0.25″ ball-bearings) with an x-raybackscatter interrogation system operating at three different sourcevoltages and various standoff distances.

Source Standoff Distance SNR SNR Voltage (feet) (Steel) (Ball Bearings)160 kV 50 77.2 47.5 100 11.5 9.8 150 3.3 2.7 450 kV 100 11.1 9.9 1.2 MV100 4.4 4.5

Calibration of the Backscatter Signal

As discussed above, some embodiments employ techniques for calibratingthe strength of the detected backscatter signal with a reference signalin order to determine whether the signal from an interrogation point islow enough to signify the presence of metal. This can be done in anumber of ways:

-   1. Determine the distance to the target object being interrogated    (for example, by using information from the video system or using a    laser range finder) and use lookup tables to determine the maximum    backscatter signal for metallic material. One disadvantage of this    approach is that the system hardware should be relatively stable.-   2. Compare the signal strength from a number of interrogation points    from objects all at approximately the same distance.-   3. Compare the signal strength from a number of interrogation points    202, 204 from different locations on the same object. This approach    is shown schematically in the FIG. 12A.-   4. Acquire a line scan 210 (shown in FIG. 12B) consisting of many    interrogation points across the object, and look for regions 208 on    the object where the backscatter brightness is significantly lower    than for the rest of the object 206. This approach is shown    schematically in FIG. 10B.

One method for simultaneously acquiring interrogation data and obtaininga reference signal is illustrated in FIG. 13. In this embodiment, thecollimation scheme, such as multiple collimators 302 allows for severalhighly-collimated x-ray beams 304 to be produced simultaneously. Arotating shutter 306, disposed within x-ray cone beam 308 produced byx-ray source 300, is then used to ensure that at any instant only one ofthe beams is actually illuminating the target object 104. For theexample shown in FIG. 13, this means that four interrogation points canbe acquired in the time that it takes the shutter to rotate through onerevolution. One advantage of this embodiment is that the speed ofoperation of the system can be enhanced, as the beam collimators do notphysically have to be re-directed between interrogation points. Thesystem may only have to be targeted once onto the central region of asuspicious object. The number of beams and their orientation withrespect to each other can be optimized for the particular target objectsbeing inspected.

One specific embodiment of the present invention operates as follows:

-   1. An operator identifies a suspicious target which he wishes to    interrogate with the system. This could be done, for example, by    clicking a mouse on the suspicious object in a video image. The    operator may wish to identify, for example, a person wearing bulky    clothing or carrying a backpack.-   2. The interrogation system then sends out a pulse of x-rays in a    highly-collimated beam, directed at the target object. By comparing    the return backscatter signal with a reference signal (using one of    the calibration methods discussed above), the system automatically    determines the threat level of the object.-   3. The system then alerts the operator, who can then determine what    further action needs to be taken. If the threat determination is    deemed to be uncertain, the system could continue to track the    suspicious target using a video tracking system, and could perform a    further confirming interrogation (if required) at a closer distance.-   4. For confirmed threats (targets with substantial metallic    content), the system may then initiate further inspection using    additional systems that employ other inspection or detection    modalities, such as x-ray backscatter imaging, mm-wave imaging, or    terra-Hertz spectroscopy. These may be used to confirm the presence    of weapons or explosives on or within the target object.

Bi-Static Compton Scatter Imaging

Equipment and methods are presented here to extend the useful range ofCompton scatter imaging systems by separating the location of the x-raydetectors from the x-ray source. In each application the detectors arecloser to the subject than the rest of the imaging system, allowing formore scattered flux to be collected than if the detectors wereco-located with the x-ray source and other equipment. The arrangement ofsource, target, and detector is analogous to many applications ofbi-static radar.

Because a number of factors figure in the ability to form images from adistance, extending the useful range of a backscatter imaging system mayprovide one or more of the following advantages: better image qualityfor a given distance, larger field of view for a given image quality ata given distance, shorter scan time to produce a given image quality ata given distance, and reduced dose to target for a given image qualityat a given distance. Long range imaging systems have a variety ofsecurity applications. Reduced dose imaging systems are particularlyimportant for the inspection of people.

An inspection system in accordance with preferred embodiments of thepresent invention is now described with reference to FIG. 14. A source12 of penetrating radiation directs a beam 20 of penetrating radiationat object 16. Source 12 of penetrating radiation is disposed, withrespect to object 16, such that the inspected field of view is less than0.1 steradians (sr). Object 16 scatters flux 22 which is detected bydetector 14. Detector 14 is disposed, with respect to the object, suchas to subtend greater than 0.5 steradians in the field of view of theobject.

Application to Inspection of Walls for Foreign Objects

In one embodiment of the present invention, now described with referenceto FIG. 15, the inspection system is configured to rapidly inspect wallsfor unwanted objects, or perform a variety of non-destructive testingapplications such as looking for flaws hidden under the body panels ofautomobiles.

FIG. 15 shows a configuration where source 12 is moved to the center ofroom 26, from which source 12 can rapidly scan walls 24 of room 26 withpenetrating radiation. Detectors 14 are placed near to walls 24. In thisconfiguration, the system can image all of the sections of walls 24 thatare not covered by detectors 14. The positions of detectors 14 can thenbe shifted to allow the inspection system to scan the remaining areas.If source 12 is not displaced when detectors 14 are moved, then bothimages can be stitched together in software to provide a modest qualityimage of room 26.

Regions that are found interesting can be scanned more closely usingtraditional methods whereby both source 12 and detector 14 are placed asclose as possible to the area under inspection.

Application to Locate People in Rooms from Adjacent Rooms

In another embodiment of the present invention, shown in FIG. 16, source12 is located in an adjacent room 28 and detectors 14 may either bebuilt into walls 24, as shown in FIG. 16, or located in adjacent rooms28, as shown in FIG. 17. Concealment of detectors may be advantageous inparticular applications. Wireless transmitters 30 can be used to connectdetectors 14 to a data processing apparatus 32 co-located with X-raysource 12.

In such a configuration, operators are able to first produce alow-dose/low-quality scan that might provide enough information toseparate perpetrators from victims. Then, if needed, higher qualityhigher-dose images could be produced of the perpetrators. In this way,high dose could be limited to a hostage taker while minimizing dose toinnocent hostages.

Application to Extend Rage of Existing Inspection Systems

As shown in FIG. 18, AS&E presently builds a backscatter imaging productknown as the Z-Backscatter Van™ (ZBV™), described, for example, in U.S.Pat. No. 7,099,434. The ZBV, designated generally by numeral 90, isoptimized for a target distance of 2-5 feet. ZBV 90 is often deployed in“portal mode”, meaning that the ZBV, with X-ray source 12 and detectors15, is stationary, while target 13 (typically vehicles) drive throughthe scanning x-ray beam 20.

In the portal operating mode, the range of the ZBV 90 is extended bydeploying additional detectors 14 nearer to target 13, as shown in FIG.18. Such a configuration may have the following advantages over relianceon ZBV's on-board backscatter detector array 15:

-   -   In the event of a detonation of the target, only auxiliary        detectors 14 would be destroyed.    -   An arbitrary number of detectors 14 could be deployed, allowing        users in the field to trade cost for added image quality when        and where needed.    -   Positions of detectors 14 can be rearranged by the user to vary        shadowing; to emphasize data from side scatter or forward        scatter; or even to produce transmission x-ray images.        Detectors 14 can transmit data to ZBV 90 electronics by using        wireless transmitters 50. The only power needed by detectors 14        is direct current provided by power supplies for the        photomultiplier tubes, which may be powered by batteries, and        power for the wireless transmitters 50. Alternately, power and        signal cables may be used to connect ZBV 90 to detectors 14.

Detectors 14 are one of the lighter components of the overall x-raysystem. A small number of auxiliary detectors can fit into the coach ofZBV 90. A larger supply of detectors can be towed in a small trailer(not shown) behind ZBV 90, or transported in other support vehicles (notshown). As shown in FIG. 19, in order to operate ZBV 90 in drive-by mode(where ZBV 90 drives past target 13 in order to scan X-ray beam 20 overtarget 13), auxiliary detectors 14 are mounted on robotic drone vehicles42. In this scenario a wireless link is used to transmit instructions torobotic drone vehicles 42, and to receive data from detectors 14.

Application Using Forward Deployed Mobile Detectors to Inspect PossibleIEDs or Left-Behind Packages

An inspection system for detecting possible improvised explosive devices(IEDs), in accordance with the present invention, is now described withreference to FIG. 20. Detector 14 is mounted on small robotic dronevehicle 42. Small robotic drone vehicle 42 brings detector 14 close toIED 40 while x-ray source 12 remains at a safe distance with theoperator (not shown). Although robotic drone vehicle 42 is a relativelyhigh cost component compared to a backscatter x-ray system, smallrobotic drone vehicles 42 designed for military applications have oftensurvived explosions, and robotic drone vehicle 42 could be furtherprotected with blast armor.

The location of detector 14 with respect to IED 40 causes differentshadowing effects in the resulting image. If detector 14 is placed ononly one side of primary x-ray beam 44, the image will have shadowsanalogous to what one would see in a photograph with the camera at theposition of x-ray source 12 and with a light source at the location ofx-ray detector 14. These shadows often prove useful in interpretingimages, as they give objects a three dimensional appearance and makecertain edges more apparent. More edges can be enhanced by movingdetector 14 to a new location, or using several detectors simultaneouslywith data from each detector 14 processed separately. Experiments atAS&E have shown that the effect can be even more useful when images fromseveral detectors at two or more angles are mixed in different ratios.

Two or more detectors 14 on two or more robots 42 can be used to fullyexploit this detector mixing concept. Alternately, after a single imageis produced using a single detector 14, detector 14 can be moved to anew location while x-ray source 12 does not move, and then a secondimage is produced. These sequential images could be combined (toincrease the effective flux) and mixed in different ratios to exploitdifferent possible shadow configurations.

Application Using Forward Deployed Mobile Detectors to Scan a Roadsidefor IEDs

A fully mobile variant of the previous embodiment is capable of‘sweeping’ for roadside IEDs, as shown in FIG. 21. X-ray source 12 ismounted on vehicle 46. Vehicle 46 may or may not be armored. A beamchopper wheel (not shown) scand beam 20 in a direction perpendicular toroad 48 while vehicle 46 drives slowly in the direction of road 48, inorder to produce a 2-D image. Detector 14 would drive ahead of vehicle46 on a small robotic drone vehicle 42. If cable management between thevehicle 46 and robotic drone vehicle 42 poses a problem, then cablingcan be replaced by wireless communication system 50 to direct roboticdrone vehicle 42 and receive signals from detector 14.

As depicted in FIG. 22, x-ray source 12 may be attached to swivel mount52, so that either side of road 48 can be imaged, or object 40 lying inroad 48 can be inspected.

Variations in the speed of vehicle 46 can cause distortions in theimage. These variations typically do not inhibit the interpretations ofbackscatter images, however, the distortions might be more problematicin long-range applications. A scan drive might be employed to regulatethe speed of both vehicle 46 carrying x-ray source 12, and robotic dronevehicle 42 carrying detector 14.

A greater challenge is posed by uneven road surfaces and bumps in theroad. These cause x-ray source 12 to bounce up and down, producingcorresponding distortions in the image. Although these distortions areusually not a problem for scans at a distance of a few feet, theireffect will grow in proportion to the distance. A change in the attitudeof the vehicle of one degree, for example, will move beam 20 only 1″ ata distance of 5 feet. However, beam 20 will be displaced by 6″ at adistance of 30 feet. A given distortion will be even more apparent(relative to existing systems) because long range systems such as thepresent invention will typically work with much smaller fields of viewthan have been used on short range systems.

In accordance with various embodiments of the invention, x-ray source 12is stabilized using the same technologies that are used to stabilize thecannon on a modern tank. Since the chopper wheel (not shown) itself islarge gyroscope, the chopper wheel may be mounted on a suspension ofgimbals and shock absorbers to minimize changes in attitude of x-raybeam 20 while vehicle 46 moves over uneven terrain.

The image is much less sensitive to changes in the position of detector14. Changes in attitude or elevation of detector 14 during a scan wouldcause only small changes in the shadowing of the image, which would notinterfere with interpretation of the image, and would likely not even benoticed.

Application for Surveillance of Select Vehicles or Persons Traversing aDefined Passageway

In another embodiment of the bi-static backscatter concept, persons orvehicles subject to inspection might be directed to traverse awell-defined region. This region might be a walkway in an airport or aroadway or tunnel through which vehicles pass.

Existing concepts for inspecting every person in such a situationrequire space for a complete backscatter source and detector adjacent tothe through-way. Moreover, subjects must pass through the beam at aspecified speed, subjects are only inspected from the side, and everysubject passing through the inspection area must be irradiated.

Situations where any one of the above constraints is unacceptable can beaddressed by a configuration such as is shown in FIGS. 23 and 24. X-raysources 12 are attached to pivoting mount 54 aimed to select anyarbitrary subset of a larger region for scanning with x-ray beam 20.

In each of these systems, operators select person 56 (in FIG. 23), orvehicle 58 (in FIG. 24), and paint only that target with X-rays. Person56, or vehicle 58, can be studied for as long as it is within passageway60 which is lined with detectors 14.

If passageway 60 is a narrow hallway, (or if the roadway passes througha tunnel) then detectors 14 can easily be concealed in walls and/orceiling or disguised as part of the walls or ceiling. In somecircumstances it might also be feasible to build detectors 14 into thesurface of passageway 60. In a configuration where detectors 14 aredeployed in the walls, floor, and ceiling of a tunnel, it is possible toachieve coverage of nearly 4 π sr, thereby making use of the greatestpossible fraction of scattered photons. Such a system achieves farhigher collection efficiency of scattered photons than currentnear-field, Compton scatter imaging systems.

As shown in FIG. 23, x-ray sources 12 may be located in the ceiling sooperators are better able to steer around uninteresting people. In FIG.25, x-ray sources 12 are drawn at the side of passageway 60. However, ina tunnel, X-ray sources 12 may also be suspended from the ceiling.

The use of multiple X-ray sources 12, or even a single x-ray source 12which can be aimed from the middle towards both ends of passageway 60,allows operators to image person 56 or vehicle 58 from multiple angles.If multiple X-ray sources 12 are aimed at the same object, or objectsthat are near to one another, then the X-ray sources 12 need to beelectronically synchronized so that at any instant, only one isshooting.

Encoders on the source-aiming mechanics may be used to identify targetlocation(s) and only allow signal from nearest detectors to beprocessed, in order to limit electronic noise and air scatter.

By imaging person 56 or vehicle 58 from a distance, speed becomes a lesscritical factor than in near field imaging systems, because angularspeed is much smaller when viewed from a distance. Imaging the targetfrom an angle that is nearly in line with the target's direction ofmotion further reduces apparent angular movement and further facilitatesthe imaging of a moving object.

Detectors 14 built into the floor or road surface, as shown in FIGS. 25and 26, must be able to support the weight of any object 80 (people,animals, or vehicles) that might move over them. Strong solid supportssuch as steel plates are typically not used on the fronts of Comptonscatter detectors because the energy of the Compton scattered x-rays istypically too low to penetrate such structures. However, structuralsupport grid 62 made of a structural material (such as steel) can beplaced over detector 14, as is shown FIGS. 25 and 26. The detectionefficiency of detector 14 will only be reduced by that fraction ofdetector area which is blocked by solid parts of structural support grid62. The structural support grid 62 will not produce artifacts of anykind in Compton scatter images, because Compton scatter x-ray images arespatially modulated by the movement of the primary x-ray beam, ratherthan by pixilation of the detectors 14, as is the case in mosttransmission x-ray and optical imaging systems.

Detector 14 may be concealed, by camouflage 64, or otherwise, in somecases, at the further expense of attenuating the x-ray signal. Inoutdoor applications, a thin layer of dirt or leaves might be used. Inan airport walkway a thin sheet of plastic with decorative patternscould obscure any identifying features of detector 14.

Application for Broad Area Surveillance

In another embodiment, shown in FIGS. 27 and 28, an array of detectors14 is located in regions of interest, and the entire region may be“painted” by single x-ray source 12.

Detectors 14 are arrayed in or on the ground in the region forsurveillance. X-ray source 12 is in a central location, able to “shoot”at all regions where detectors 14 are located. This way X-ray flux usedfor imaging each pixel of a given target is roughly independent ofdistance, because no matter where in the region object 82 stands, object82 is still roughly the same distance from the nearest detectors 14.X-ray source 12 might scan azimuthally through as much as 360 degrees,in a manner similar to a radar system.

In this continuous sweep mode, once the scan area is surveyed, thebackscatter signal at any point should not change unless a new objectwere introduced. Therefore, a computer could monitor the image, or justthe integrated signal from any given region in the image, and alerthuman operators in the event of a change. A sudden increase in imagedensity might indicate the presence of a living intruder (person oranimal). More subtle changes might indicate motion of objects (e.g.vehicles entering the region, or movement of camouflaged people/vehiclesthat have been hiding in the region since before the scan started).Alternately, an optical or infrared imaging system might be used in asimilar way to automatically detect potential threats. Once a potentialthreat is flagged, the system could automatically begin a more detailedCompton x-ray scan to produce an image to be analyzed by a humanoperator.

Pressure sensors (not shown) might be integrated with detectors 14 inthe ground. In this case, the pressure sensors would be the firstdetection system. Then a computer might automatically aim the X-ray beam20 at the region in question and produce an image.

A continuous sweep mode may also be used to scan a crowd for potentialsuicide bombers.

Pressure sensors integrated with detectors 14 and placed in the groundaround detectors 14 may be used to sense when object 82 is moving inparallel with the path of the beam. This information can be used by anautomatic safety system to limit the dose to object 82 by shutting offbeam 20 or changing the sweep path. The best solid angle coverage isachieved with a tiled pattern of detectors 14 ‘carpeting’ the ground.

In certain embodiments of the invention, detectors 14 may be camouflagedby thin layer of dirt, or otherwise concealed, although some forms ofcamouflage may result in a reduction in signal. Alternatively, oradditionally, detectors 14 may also be hidden in above-ground objectssuch as artificial rocks or trees, although a large solid angle coveragewould be unlikely in this case.

Detectors 14 may be deployed as free standing monoliths 68, as shown inFIG. 29, though a large solid angle would require filling much of thearea with monoliths 68, which might obstruct visual lines of sight fromx-ray source 12 to potential targets of interest. Building 70 and othersensitive structures might have detectors 14 mounted on the buildingwalls.

Electronic noise could be limited by only processing signals from thosedetectors 14 that are near the target of the x-ray beam 20.

If the beam 20 is fired directly towards a detector 14, that signal isprocessed separately, as it would be predominantly a transmission imagesignal rather than a Compton scatter signal. Encoders on the sourcepositioning device could indicate the position of the x-ray beam spot inorder to indicate to the control system when detector 14 is in thedirect path of beam 20.

The electronics and software are designed to allow the user to deployand configure any number of detectors 14 in any chosen configuration.Different terrain and different applications would require differentconfigurations and numbers of detectors 14.

Air scatter becomes a more important consideration when scanning at adistance. Detectors 14 near to the primary beam 20 receive an airscatter signal which will ‘fog’ the image. The noise caused by thiseffect might be mitigated by reading the signals from detectors 14 atdifferent distances in separate channels 74, as is shown in FIG. 30, sothat person 76 is imaged in only one detector, and that image containsonly the air scatter background from that detector (or the set ofdetectors in that region). Detectors 14 located along the path of theprimary beam 20 which are not near to the target receive much lesssignal from the target and therefore have a much higher ratio of noiseto signal. The overall signal-to-noise ratio would be improved byignoring the entire signal from these detectors.

Although various exemplary embodiments of the invention have beendisclosed, it should be apparent to those skilled in the art thatvarious changes and modifications can be made which will achieve some ofthe advantages of the invention without departing from the true scope ofthe invention.

What is claimed is:
 1. An inspection system for inspecting an object,the system comprising: a. a conveyance characterized by an enclosingbody; b. a source of penetrating radiation contained entirely within theenclosing body of the conveyance for generating penetrating radiationincident upon the object while the object is disposed externally to theenclosing body; c. an uncollimated detector contained entirely withinthe body of the enclosed conveyance, for generating a scatter signalbased on penetrating radiation scattered by the object; and d. acontroller for ascertaining a specified characteristic of the objectbased on the scatter signal.
 2. An inspection system according to claim1, wherein the specified characteristic of the object ascertained by thecontroller is an atomic number characterizing material contained withinthe object.
 3. An inspection system according to claim 1, wherein thesource of penetrating radiation includes a spatial modulator for forminga flying spot beam.
 4. An inspection system according to claim 1,additionally comprising at least one detector disposed externally tosaid enclosing body.
 5. An inspection system in accordance with claim 1,further comprising at least a second detector for generating the scattersignal.
 6. An inspection system in accordance with claim 1, furthercomprising a transmission detector for generating a transmission signal.7. An inspection system in accordance with claim 6, wherein thetransmission detector includes an L-shaped detector with a verticalsection and a horizontal section.
 8. An inspection system in accordancewith claim 6, wherein the transmission detector is incorporated into aspeed bump structure.